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Analysis power supply noise and noise margin

Apr 9th, 2014

There are many thousands of transistors within the chip , the gates of transistors within the circuit , combinatorial logic , registers, counters , delay lines , state machines , and other logic functions. With the increasing integration of the chip , increasing the number of transistors inside . A limited number of external pins of the chip to provide a separate supply pin is impractical for each transistor. Chip to the external power supply pin provides a common internal transistor power nodes , thus converting the status of the internal transistor power would inevitably lead to noise transfer inside the chip.
The internal operation of each transistor is usually synchronized by the core clock or on-chip peripheral clock , but due to differences in the internal delay , the state transition of each transistor can not be strictly synchronized, when some transistors state transition has been completed , while others transistor may still be in the conversion process . Chip at a high level power supply noise will pass gate circuit to the input portion of the other gate . If you accept the power supply noise gate in an indeterminate state at this point level conversion area , then the power supply noise may be amplified and generate rectangular pulse interference at the output of the gate , thereby causing the circuit logic errors . External power supply pin chip noise at the circuit through the dissemination within the department , but also may trigger internal registers to produce state transitions.
In addition to its impact on the chip operation state, the power supply noise will affect the other part. For example, power supply noise can affect jitter crystal oscillator , PLL, DLL , the conversion accuracy A / D converter circuit and so on.
Due to inconsistencies in the final product as well as the operating temperature changes in the production process , and if the problem is due to the power generated by the system , the circuit will be very difficult to debug , so it is best to follow in the beginning of the circuit design of a sophisticated design rules , the power the system more robust.
The vast majority of chips will be given a working voltage range , this value is typically ± 5%. For example : For a 3.3V voltage , in order to meet the chip to work properly, the supply voltage between 3.13V to 3.47V, or 3.3V ± 165mV. For 1.2V voltage , in order to meet the chip to work properly, the supply voltage between 1.14V to 1.26V, or 1.2V ± 60mV. These restrictions can chip datasheet part of recommended operating conditions found . These limitations should be considered in two parts , a first DC output voltage error of the chip, the peak amplitude of the second power supply noise . Vintage regulator chip output voltage accuracy is typically ± 2.5%, so the peak amplitude of the power supply noise should not exceed ± 2.5%. Of course, with the improvement of chip technology, the higher the precision of modern DC voltage regulator chip , may reach ± 1% or less, and Texas Instruments (TI) company’s switching power supply chip TPS54310 accuracy up to ± 1%, linear regulator can source AMS1117 up to ± 0.2%. But remember, to achieve this accuracy is conditional, including load, temperature and other restrictions . Therefore, reliable design to ± 2.5% or more capture some of this value . If you can make sure that the chip used in the circuit board can be installed to achieve higher regulation accuracy , then you can design your The noise margin is calculated separately. The following section focuses on the design principle of the power of description , power supply noise margin will use this value ± 2.5% .
Power supply noise margin calculation is very simple , as follows:
For example, the chip between the normal operating voltage range of 3.13V to 3.47V, the nominal output voltage regulator chip 3.3V. After installing the circuit board, the chip output voltage 3.36V. So allowable voltage range of 3.47-3.36 = 0.11V = 110mV. Chip output voltage accuracy of ± 1%, ie ± 3.363 * 1% = ± 33.6 mV. Power supply noise margin is 110-33.6 = 76.4 mV.
Calculation is very simple, but to pay attention to four issues:
First, the output voltage can be precisely regulated chip set at 3.3V it? Peripheral devices such as resistors and capacitors inductance parameter is not accurate , which affects the output voltage regulator chip , so here with a 3.36V this value. Before installing the circuit board, you can not predict the exact value of the output voltage .
Second, the work environment meets the recommended environmental regulator on chip manual ? What parameters will be consistent and chip manual on the device aging ?
Third, the load situation? This output voltage regulator chips also have an impact .
Fourth, the power supply noise will ultimately affect the signal quality. The source of the noise signal is not just supply noise , crosstalk and other signal integrity issues reflection , the noise will be superimposed on the signal , can not put all the noise margin is allocated to the power system . Therefore, in the design of power supply noise margin when to leave room .
Another important question is: different voltage levels , power supply noise margin requirements are not the same, according to ± 2.5% if calculated , 1.2V voltage level of noise margin is only 30mV. This is a very harsh restrictions , to be cautious when designing . Analog circuits for higher power requirements . Power supply noise clock system , may cause timing matching problem . Therefore, you must pay attention to power supply noise problem.

Design and implementation of current-voltage power supply’s voltage feedback circuit

Apr 9th, 2014

In the conventional voltage- controlled , only one loop , poor dynamic performance . When the input voltage disturbances caused by voltage feedback loop duty cycle changes more slowly. Therefore, the required output voltage error is smaller occasions transient voltage- control mode is not desirable . To solve this problem , you can use current- control mode. Current- voltage- control not only retained control of the output voltage feedback , but also increases the inductor current feedback ; And the current feedback control on the PWM converter ramp function , eliminating the need sawtooth generator , the system ‘s performance has obvious superiority. Features current-mode control method is as follows :
1, the system has a fast input and output dynamic response and high stability ;
2, high output voltage accuracy ;
3, with the internal current of the power control switch ;
4, good parallel operation capability. As the rate of change of inductor current didt feedback directly follows the input voltage and the output voltage changes. Voltage feedback loop , the output of the error amplifier as a current reference signal , compared with inductor current feedback directly controls the duty cycle of the power switch is off , the voltage current-mode power supply design feedback is very important issue. This paper describes the use of current-mode controller chip uc3842 , the voltage feedback circuit design.
uc3842 Introduction
Figure 1 is a block diagram showing the internal structure of the controller UC3842PWM . Its internal reference circuitry generates +5 V reference voltage as the UC3842 internal power supply, 2.5V voltage was attenuated as the basis of an error amplifier , and a power supply circuit output 5V/50mA . The oscillator generates a square wave oscillator , the oscillation frequency depends on the external timing element is connected between pin 4 and pin 8 is connected between the resistor R and the capacitance to ground pin 4 and C together determine the oscillation frequency , f = 1.8/RC. The feedback voltage from 2 feet to the inverting terminal of the error amplifier . A pin external RC network to change the closed-loop error amplifier gain and frequency characteristics , 6 -pin output drivers switch square wave as a totem pole output . 3 feet for current detection terminal for detecting switch current , when the 3 -pin voltage ≥ 1V, UC3842 closed output pulse overcurrent protection switch will not be damaged. UC3842PWM controller features undervoltage lockout circuit open threshold 16V, turn off threshold is 10V. For this reason , the oscillation circuit can be effectively prevented when working in the vicinity of the threshold voltage .

UC3842 has the following characteristics :
1, a small number of pins, the external circuit is simple , inexpensive ;
2, good voltage regulation ;
3, significantly improved load regulation ;
4, the frequency response characteristics of a good , stable amplitude ;
5, with overcurrent limit , overvoltage and undervoltage lockout feature.
UC3842 has a good line regulation , because the input voltage Vi changes immediately react to changes in the inductor current , it does not undergo any error amplifier output pulse width can be changed in the comparator , and then increase the level of the output voltage Vo to the error amplifier control , enabling better line regulation ; may significantly improve load regulation, specifically because of the error amplifier can be used to control due to load changes caused by the output voltage changes, especially so when the amplitude of the light load voltage increases greatly reduced . Outer error amplifier circuit of the compensation network is simplified, improved stability and improved frequency response , greater gain-bandwidth product . The current limit circuit is simplified , since the peak inductor current sensing resistor , it can restrict the natural formation of by- pulse circuit , as long as Rs level reaches 1V, PWM off immediately , and this peak inductor current sensing technology can be sensitive to restrictions the maximum current output .
Common voltage feedback circuit UC3842
1, the output voltage of the direct voltage as the error amplifier input
The output voltage Vo after two resistor divider as a sampling signal input UC3842 pin 2 ( inverting input of the error amplifier ) . Figure 2 .
The advantage of this circuit is that the sampling circuit is simple , the drawback is the input voltage and the output voltage must be total , can be electrically isolated. Bound to cause difficulties power supply wiring and high-frequency switching power supply in the state , prone to electromagnetic interference , inevitably difficult circuit design , so this method is rarely used.

2, the auxiliary power supply output voltage divider as the error amplifier input
Induced voltage generated on the single-ended flyback transformer auxiliary winding T increases as the output voltage increases, the voltage is rectified , filtered and regulated DC voltage network to get and give UC3842 power supply. Meanwhile, the voltage after two resistor divider as the sampling voltage , into the UC3842 feet 2 .
When the start UC3842 If the feedback windings not provide sufficient UF, the circuit will start to stop , belching phenomenon . In addition , based on experience , if UF is greater than 17.5V, UC3842 work can also cause abnormal , causing the output pulse duty cycle decreases, the output voltage is low . Therefore the selection of the feedback winding and the winding turns is very important , generally 13 ~ 15V can be designed so UC3842 normal operation, the voltage is maintained at about 7 feet 13V.
The advantage of this circuit is simple sampling circuit , the secondary winding , the primary winding and not between any of the auxiliary winding of the electric path , easy wiring . The disadvantage is not obtained directly from the secondary winding sampled voltage regulator ineffective, the experiment found that when the power load change is large, basically can not achieve regulation . This circuit is suitable for the case of a fixed load . 3 , using a linear optocoupler change the voltage error amplifier input error
Shown, the switching power supply with two voltage sampling circuit shown in Figure 3 : a rectifier , filter and regulator through one of the auxiliary winding voltage D1, D2, C1, C2, C3, R9 consists of the DC voltage of 16V to UC3842 power supply, in addition , after the voltage voltage divider R2 and R4 to get a sample voltage , which mainly reflects the way the sampling voltage DC bus voltage changes ; another way is optocouplers, three-terminal adjustable regulator Z and R4, voltage sampling circuit R5, R6, R7, R8 composed circuit voltage reflects the change in output voltage ; when the output voltage increases , after the voltage divider resistors R7 and R8 Z reference input voltage increases , the regulator the voltage value increases, the current through the optocoupler lED current decreases , the current flowing through the phototransistor of the optocoupler is also reduced accordingly , a feedback error amplifier input voltage is reduced , resulting in a drive signal output pin 6 UC3842 the duty cycle is smaller, so the output voltage drops to achieve the purpose of regulation .
The circuit because the use of optocouplers to achieve the output and input isolation , the weak and the strong electrical isolation , reduced electromagnetic interference , strong anti-jamming capability , and is sampling the output voltage , the regulator has good performance . The disadvantage is that external components increase, increasing the difficulty of wiring , increasing the cost of the power supply.

Optocoupler and voltage reference using feedback control circuit
To meet the power requirements of a large load changes when . Improve the stability of the output voltage , the design of a sample from the secondary winding of the output of the feedback control circuit . Circuit shown in Figure 4 : Sampling and feedback circuit from voltage optocoupler PC8I7, TL431 and RC network connected to it constitute . The control principle is as follows : ? Output voltage by RIJ, R after partial pressure sampling voltage , this voltage is sampled and TL431 provided 2.5 V reference voltage. When the output voltage is normal (5 V) , the sampling voltage of 2.5V reference voltage TL431 offers equal, the TL431 ‘s K constant electric potential . Optocoupler diode current flowing through the constant flow of current through the optocoupler CE unchanged . UC3842 feet a potential stable , the duty cycle of the output driver constant, stable output voltage setpoint change. When the output voltage of 5 V is high because for some reason when , after the divider resistors RIJ, R? Partial pressure value is greater than 2.5 V, the TL431 ‘s K electrode potential drop , flowing through the optocoupler diode current is increased, the flow CE increase the current through the optocoupler . UC3842 a potential drop foot , the drive pulse output pin 6 of the duty cycle decreases, the output voltage is reduced, thus completing the feedback regulation process. When using UC3842 to control the duty cycle of the switching power supply , conventional network usage is between plus R 2 feet UC3842 feedback optocoupler TL431 and other components and the power control loop , the C electrode of the optocoupler UC3842 to the pin 2 as the output voltage feedback. The circuit shown in Figure 3 does not use such a connection , but the optocoupler UC3842 C is directly connected to the electrode pin as an output voltage feedback , pin 2 is directly grounded. UC3842 foot 2 is the inverting input of the error amplifier inside , pin 1 is the output of the error amplifier . This connection method skips the UC3842 internal amplifier , because the amplifier for signal transmission has its transmission time , while the output and input are not established , not UC3842 internal amplifier. The advantage is that the feedback signal of the transmission amplifier Processed shortened transmission time , so that the dynamic response of the power faster. In addition , TL431 itself an internal high gain error amplifier , but it is isolated from the high pressure side , so the feedback signal after amplifier and optocoupler TL431 UC3842 within the direct control of the internal error amplifier output ( pin 1 ) , the control accuracy does not decrease . The use UC3842 internal error amplifier , the feedback signal is continuously through two high gain error amplifier increases the transmission time . The circuit is then fed back to the UC3842 feet through optical isolation by sampling an output terminal , skip the UC3842 internal amplifier , reducing the transmission time for the dynamic supply response faster. While using TL431 internal high gain error amplifier , to ensure high control accuracy. This simple circuit topology , fewer external components, and the voltage sampling circuit using a three -terminal adjustable voltage reference, the output voltage changes in a large load occurs, the output voltage is substantially unchanged. Experimental results show that the circuit has good voltage regulation .
Epilogue
You can select different ways according to the specific requirements of feedback . But for multi-output feedback circuit , because each output for different applications requiring output accuracy is different, so the feedback positive polarity output end of each accounting for the proportion of the amount of feedback is also different . According to the specific requirements of the application to meet specific design requirements , such as the requirement of two +5 v +12 v output voltage is positive , since the former is often used in the case of relatively high accuracy , so that the proportion of relatively large share of feedback , preferably 60% , which is taken as 40% . As a number of outputs, so in the secondary winding of the overlay technique can be used to reduce the transformer winding turns .

high voltage power module for APEX PA91 92 93

Apr 1st, 2014

high voltage for PA91We have a high voltage power module for APEX PA91.It can output 0 upto 200VDC and current is 4MA max.
Specifications: 50x38x25mm
Technical parameters:
Input voltage: DC12V ± 10%
Output voltage: 0 ~ positive 200VDC
Output Current: 4mA
Output accuracy: 0.1%
Control mode: the coil of the external 10K potentiometer
Package: lead


Download the datasheet for PA91


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DC high voltage power supply range of applications

Apr 1st, 2014

high voltage powerDC high voltage power supply is AC power or three-phase power input , or more than a few tens of volts or more volts DC voltage output of the power supply , the output power of several hundred watts to several kilowatts , and can be regulated or steady flow . Earlier DC high voltage power supply is three-phase AC power or high voltage transformer boost the frequency becomes high voltage alternating and direct current high voltage rectifier filter to get . Since the frequency is low, the power larger than the size and weight , the conversion efficiency and poor stability . With the switching power supply technology development and maturity , using high-frequency switching power conversion technology with the characteristics of high-voltage direct current high voltage power supply developed into the mainstream . It features small size, light weight, high efficiency , high power , low ripple , low and high storage stability, high reliability. In order to meet the requirements of different use , some DC high voltage power supply steady flow automatically converted into the form of power for a variety of devices.

For analytical instruments light class power , such as deuterium lamp power, xenon lamp power supply, zinc lamp power supply, etc. , but also for the tube type of equipment supply, such as photomultiplier tubes, avalanche control , electron gun , X-ray tube , the above two types of power company have done little ripple small volume , high precision , suitable for various types of equipment used.

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photomultiplier tube base’s categories

Mar 31st, 2014

high voltage base for PMT
We often supply high-voltage power to customer.but some customer need PMT base with our high-voltage power ,but the customer do not know what kind of base is suit for his PMT.
Here I’d like to introduce a general kind
(1) pure pin coupling, without any electrical function;
(2) with a partial pressure module;
(3) with a partial pressure module and miniature high-voltage module;
(4) with a partial pressure, hypertension and pre-amplifier module;
and how can we select the base?
Depending on your PMT function,Output function,Work Environment.
We provide customized services.

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