![]() ![]() LED D2 provides a visual indication when the circuit is running in the constant current mode. POT R10 can be used to adjust the output current while POT R11 can be used to adjust the output voltage. C6 is the input filter capacitor while C9 is the output filter capacitor. Resistor R16 limits the input current to the LM317 and base current to the transistor Q5. The output voltage of the regulator circuit is fed back to the non inverting input of the opamp while output voltage of the opamp is fed back to the inverting input of the opamp itself through capacitor C7. Diode D3 and capacitor C3 forms a compensation circuitry for the opamp. In addition to LM317, LM310 a single operational amplifier is also used in the circuit. Such a circuit is a very inevitable gadget on the work bench of an electronic enthusiast. The circuit shown above is of a 5A constant current / constant voltage regulator using LM317. 5A constant current constant voltage regulator.ĥA constant current constant voltage regulator Resistor R4 sets the maximum output voltage and it is according to the equation V out Max = 1.25V (1 + (R4/R3)) + (Iadj x R4). The width of each step depends on the value of the resistors you choose. Addition of each resistance in parallel to the R4 will reduce the effective resistance of the path and so the output voltage of the resistance will decrease in steps. Logic high at terminal A will make Q1 ON and so resistor R5 will be added parallel to R4 and so on. In simple words the output voltage will be according to the logic level of the digital inputs A, B, C and D. Parallel to the resistor R4, four more resistor branches each with a transistor switch is added and these resistors can be included or excluded in to the circuit by making the corresponding switching transistor ON. The circuit is a just a modification of the ordinary voltage regulator using LM317. LM317 voltage regulator with digitally selected outputĪ very simple adjustable regulator circuit with digitally selected output is shown above. Adjustable regulator with digitally selected output. The output voltage of the regulator circuit depends on the equation, Vout = 1.25V (1 + (R2/R1)) + I adj R2. ![]() C1 is the input filter capacitor while C2 is the output filter capacitor. Resistor network comprising of R1 and R2 connected in association to the pin1 (adj) is used to set the output voltage. Input voltage is fed to the pin3 (v in) of the IC and regulated output voltage is available from pin 2 ( V out) of the IC. If you don't want constant current operation, then why not have fold-back current limiting? Once the over current protection is tripped, the current through the transistor can be reduced, to both save power and keep it within its safe operating area.A classic voltage regulator circuit using LM317 is shown above. The problem with dropping excessive voltage across BJTs is passing any appreciable current for a reasonable period of time, exceeds the safe operating area of the device, resulting in secondary breakdown and lots of smoke. IMHO, it has the following advantages: - input voltage can be up to 400V - output voltage from 2.5V to Input voltagev - 20V - exact current limiting - output current could be up to a feq amps, depending on power FET used, voltage difference and (fan) cooling - low ripple Some info can be found at: or here : or here: - this is where I got the idea from, thanks, Alex.Īnother transistor can be added to the circuit I posted previously, to boost the current too. After some bad and smelly experiences with the National Semiconductor LM317 high voltage example circuit (same as you have below) I tried a TL431 based one with a well-cooled linear MOSFET pass element. ![]() Transistor SOAR will be an important limiting factor then. When I get you correctly, your output current requirement is a few Amps, this means you have to use external pass elements anyway just because of dissipation, especially when the output get shorted. Hi, both the LM317 and the TL783 are not extremely robust at high voltages. ![]()
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