LM334S in series for higher voltage

Hi,

Can I serialise multiple LM334S to have a 160V 1µA current source?

Thank you in advance

Best

Nick

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  • +1
    •  Analog Employees 
    on Nov 18, 2019 1:02 AM

    Hi Nick,

    Running several LM334s in series can be done, but there needs to be a thought given to the matching that comes with doing this. The problem that happens is that when you run one in serial with another, the current through each one will vary slightly based on part-to-part variations together with external component variations. When this happens, the devices that want to run lower current will go high impedance compared to the parts running higher current. When this happens, the lower current devices will have the voltage across them rise until they violate the absolute maximum rating and go into breakdown unless some protection is employed. The easiest thing to do is to add a Zener diode across each current source, with a typical Zener voltage below the 30V absolute maximum rating of the LM334. A higher current part, the LT3092, has an application that shows this on page 16 of its data sheet.

Reply
  • +1
    •  Analog Employees 
    on Nov 18, 2019 1:02 AM

    Hi Nick,

    Running several LM334s in series can be done, but there needs to be a thought given to the matching that comes with doing this. The problem that happens is that when you run one in serial with another, the current through each one will vary slightly based on part-to-part variations together with external component variations. When this happens, the devices that want to run lower current will go high impedance compared to the parts running higher current. When this happens, the lower current devices will have the voltage across them rise until they violate the absolute maximum rating and go into breakdown unless some protection is employed. The easiest thing to do is to add a Zener diode across each current source, with a typical Zener voltage below the 30V absolute maximum rating of the LM334. A higher current part, the LT3092, has an application that shows this on page 16 of its data sheet.

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