| Electronics > Projects, Designs, and Technical Stuff |
| minimum load circuit for lab psu |
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| nemail2:
Hi in this: https://www.eevblog.com/forum/projects/how-to-wiregnd-everything-correctly-to-get-accurate-adc-readings-in-my-project/msg2439009/#msg2439009 project I'm looking for a solution to constantly draw about 6mA or so to have a minimum load which helps stabilize everything. LM334 doesn't work out cause it only works down to about 1V when set to about 6mA My currently used circuit (T8, D11, R25, R46) doesn't work quite well either and the zener diode gets really hot (above 75 °C). The circuit in the attachment works, but it needs -5V which I don't have. I wanted to avoid adding additional switching noise by a, say TC7660 or something like that to generate the negative voltage. Does anyone know of an off the shelf solution for this? The circuit in the screenshot works really nice even down to 0V. Thanks! |
| Jay_Diddy_B:
Hi, You can try a current mirror circuit like this: This works well if the V2 is greater 100mV, which is pretty good. The circuit will not work as well in practice because the two transistors are not at the same temperature. The temperature of Q1 is a function of the output voltage of the power supply. I have attached the LTspice model. Regards, Jay_Diddy_B |
| NiHaoMike:
The classic electronic load circuit with an opamp and MOSFET would work nicely down to very close to 0V. |
| schmitt trigger:
For the current mirror that Jay_didy suggests, you may find low cost, dual matched pairs from both Nexperia and OnSemi. Do a parametric search on their websites. They should be more than enough for your requirements. Of course, if you want to splurge and money is not an issue, then the MAT01 from Analog Devices is for you. |
| Jay_Diddy_B:
Hi here is the model for the scheme proposed by NiHaoMike: This depends on the op-amp working with the inputs near the -ve rail. Some op-amps work well like this others do not. Check the common mode range of the inputs and input bias currents etc. I chose 60mV across the shunt to get away from input offset and input offset drift. I have attached the model. Regards, Jay_Diddy_B |
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