Linear voltage regulators & three-terminal types

A linear voltage regulator holds its output steady by burning off the difference between input and output as heat — simple, quiet, and predictable. This page explains how the family works, how three-terminal parts and the 78 series fit in, and how to specify a linear regulator when you buy from Haiben. Haiben is a Shenzhen-based electronic components supplier founded in 2013; our own-brand semiconductor line, Weforsemi, is operated by our wholly-owned subsidiary, and exact part numbers and datasheet values are confirmed at quotation.

Linear voltage regulators in one view

A linear voltage regulator is a closed-loop circuit: a pass element, a voltage reference, an error amplifier and feedback. The loop adjusts the pass element so the output stays at the set point as load and input vary. Because the pass element sits in series and dissipates (V_in − V_out) × I_out, efficiency falls as the input-to-output gap grows. In exchange, the output is free of switching ripple, the external part count is small, and the design is easy to stabilise.

That trade-off sets where linear regulation earns its place: analogue and sensor rails, reference and bias supplies, post-regulation after a switching stage, and any node where noise matters more than efficiency. Our power management ICs catalogue covers the full range, organised as Low-Dropout Regulators (LDO); Buck DC/DC Converters / Step-Down; Boost DC/DC Converters / Step-Up; LED Drivers; Three-Terminal Voltage Regulators; Overvoltage Protection ICs (OVP); Lithium Battery Charging ICs; and Serial Flash ICs on its own page.

Three-terminal regulators and the 78 series

A three-terminal regulator is the simplest fixed-voltage form: input, output and ground, with the set point fixed inside the part. The 78 series — positive fixed outputs in the common 5 V, 9 V, 12 V and 15 V steps — is the textbook example, and it remains a sensible default for low-cost rails that need no adjustment. The 79 series covers the negative side. Adjustable variants replace the ground pin with a feedback node, letting two external resistors set the output.

Three-terminal parts are selected on input voltage headroom, output tolerance, quiescent current, thermal resistance and package. They need a dropout of roughly 2 V or more between input and output to regulate reliably, so check headroom at the lowest input, not the nominal one. Where the input is only a few hundred millivolts above the output, a three-terminal part will not hold regulation and a low-dropout device is the right choice. For simple shunt references built from a reverse-biased diode, see a Zener diode as a voltage regulator.

Linear vs low-dropout: the division of labour

The two families differ mainly in pass-element topology. Classic three-terminal regulators use an NPN Darlington pass stage, which needs several volts of headroom. A low-dropout regulator uses a PNP or PMOS pass element that can regulate with a few hundred millivolts or less across it. The LDO also brings its own stability questions — output capacitor ESR and value, transient response, and quiescent current — that the classic 78 series largely avoids.

In practice the split is straightforward: keep the standard linear regulator where headroom is ample, cost matters and noise is modest; move to an LDO when the input is close to the output, when running from a battery, or when the load steps quickly. This page covers the general linear regulator and the three-terminal/78-series case; the low-dropout specialisation sits on our LDO regulators page, where the selection criteria specific to LDOs are set out. The Weforsemi line lists LDOs, charging ICs, DC-DC boost ICs, DC-DC buck ICs, backlight driver ICs and LED driver ICs; for regulators, LDOs and three-terminal parts are the relevant categories.

Specifying a linear regulator

Regulator datasheets are only meaningful against a defined operating envelope, so fix the following before requesting a quote:

• Input voltage range, including the minimum under load and the maximum transient.
• Output voltage and tolerance, and whether it is fixed or adjustable.
• Load current, steady-state and peak, with duration.
• Dropout requirement at the worst-case input.
• Quiescent current, especially for always-on rails.
• Thermal budget: ambient, package, copper area and expected dissipation.
• Noise and ripple limits, plus PSRR at the frequencies your load is sensitive to.
• Output capacitor value and ESR (stability), and required protection features.

State plainly: exact part numbers and datasheet values for our LDO and linear regulator range are confirmed at quotation. Where a design needs clamping rather than regulation, the OVP family is separate; the only part with published model-level detail is the VCP14C13P-A, a SOT23-3 overvoltage protection IC in the 1.3 A class. Send your operating envelope with the enquiry and our engineers will confirm matching Weforsemi options.

Frequently asked questions

Is a linear voltage regulator the same as an LDO?

No. Both regulate linearly, but an LDO uses a low-dropout pass element and can hold regulation with only a small input-to-output gap, while a classic three-terminal regulator needs more headroom. Choose the LDO when the input is close to the output or the supply is a battery.

Do you publish regulator part numbers and datasheet values online?

We publish catalogue categories, and the Weforsemi line lists its product families. Exact part numbers and datasheet values for our regulators are confirmed at quotation so each recommendation matches your input range, load and thermal budget rather than a generic figure.

Can you supply OVP parts as well as regulators?

Yes. Overvoltage protection ICs are a separate catalogue category. The one part with published model-level data is the VCP14C13P-A in a SOT23-3 package, rated in the 1.3 A class; other OVP options are confirmed at quotation.