I'm a newbie that happened to make a home-made solar panel that outputs 18V and 6A without a load. I'm planning on charging a 12V battery bank through an MPPT or PWM. I've been researching what type of blocking diode I should put on my solar panel and I'm getting confused.

I have a couple Zeners on hand, but I know the reverse voltage on them is far too low. I found out that Schottky diodes are often used as bypass diodes for solar cells, but read that they also have low reverse voltages and high reverse leakage current which didn't sound suitable for a blocking diode. Normal silicon diodes seem workable, but I don't like the voltage drop of ~0.7V compared to the Schottky's ~0.45V.

So what diode should I use? Should I just take the hit and lose 0.7V with the silicon diodes? Or is this a moot point because the MPPT/PWM would take care of this (if so, what if I wasn't using an MMPT/PWM)?

Thanks in advance. Cheers!

  • \$\begingroup\$ is 6A the short circuit current or the ideal MPT load \$\endgroup\$ – Tony Stewart EE75 May 11 '17 at 0:43
  • \$\begingroup\$ the short circuit \$\endgroup\$ – Mr. Cheezits May 11 '17 at 12:07
  • \$\begingroup\$ I have an open loop MMPT model somewhere that draws ideal current depending on Voc and Isc for a known Vmp that changes with input current from solarity. Some use Iin/Isc ratios around 80% then use pulse Isc to measure solarity. I used a nonlinear diode current controlled MOSFET to load the PV to MPT and use a PD to measure solarity. \$\endgroup\$ – Tony Stewart EE75 May 11 '17 at 13:05

This is a preferred solution.

enter image description here



  • \$\begingroup\$ This is a pretty nifty solution. But what would prevent the breakdown of the Zener diode when the current is moving from the MOSFET to the load? Wouldn't it happen if the voltage difference between the battery and Vin is large? \$\endgroup\$ – Mr. Cheezits May 11 '17 at 12:21
  • \$\begingroup\$ the Zener is supposed to "breakdown" i.e. conduct Rg current. to limit the gate voltage to Vz and included to protect the Vgs \$\endgroup\$ – Tony Stewart EE75 May 11 '17 at 13:02
  • \$\begingroup\$ I understand the function, but let's say the voltage at the source node is greater than Zener breakdown voltage i.e. (V_solar - V_DS - V_Load > V_Reverse_Zener). Wouldn't it activate the gate? \$\endgroup\$ – Mr. Cheezits May 11 '17 at 13:50
  • \$\begingroup\$ Yes since this shows protecting passive load from reversed battery, so swapping Vbat and active PV Load protects PV & battery from reversed current. Values still need to be calculated for RdsOn, Vz, Rg. Then you can get fancy with PWM and inductor for PMT control and charge Voltage control... but that's another question. \$\endgroup\$ – Tony Stewart EE75 May 11 '17 at 15:43
  • \$\begingroup\$ @Mr.Cheezits try this and vary the slider for Solar input tinyurl.com/kw8ke6r \$\endgroup\$ – Tony Stewart EE75 May 12 '17 at 0:17

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